Base station, mobile station, and power control method

ABSTRACT

A base station includes: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. Accordingly, irrespective of transmission power history over a past continuous time, the mobile station receives an instruction on the transmission power from the base station each time when transmitting a packet so as to be able to adjust the transmission power.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of and, thereby,claims benefit under 35 U.S.C. §120 to U.S. application Ser. No.11/917,341, entitled, “BASE STATION, MOBILE STATION, AND POWER CONTROLMETHOD,” which is a national stage application of PCT Application No.PCT/JP2006/311874, filed on Jun. 13, 2006, which claims priority to JP2005-174395 filed Jun. 14, 2005 and JP 2005-241902 filed Aug. 23, 2005.The contents of the priority applications are incorporated by referencein their entirety.

TECHNICAL FIELD

The present invention generally relates to radio communication. Moreparticularly, the present invention relates to a base station, a mobilestation and a method for controlling transmission power of a sharedcontrol channel used for packet switching type communication.

BACKGROUND ART

In a mobile communication system such as IMT-2000, transmission powercontrol is performed from the viewpoint of enlargement of circuitcapacity and economy of battery of a mobile station and the like. Forexample, quality measurement of a channel is performed in a receivingside, and a transmission power control (TPC) bit is transmitted by areturn channel (DPCCH, for example) such that the channel that is beingreceived satisfies desired quality. As a result, the transmission poweris updated by 1 dB, for example, and quality measurement andtransmitting/receiving of the TPC bit are repeated, so that thetransmission power can be gradually changed to be closer to an optimalvalue. That is, in a communication of a circuit switching scheme, anindividual channel is assigned specifically to a mobile station, and thetransmission power of the mobile station is gradually adjusted based ona temporally continuing history on the transmission power. Suchtransmission power control is described in a non-patent document 1, forexample.

-   [Non Patent document 1] Keiji Tachikawa, “W-CDMA mobile    communication scheme”, MARUZEN, pp. 126-128

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

In a future mobile communication system, a packet switching typecommunication scheme is adopted in place of the conventional circuitswitching type communication scheme. Radio resources of a packet formare shared by a plurality of users, and availability of the radioresources is properly scheduled in a base station. In such a mobilecommunication system, there is not only a mobile station to which theradio resources are actually assigned but also a mobile station thatdesires assignment but to which the resources are not yet assigned. Inaddition, such a situation arises in circuits of both of uplink anddownlink. For causing a mobile station placed in various operationsituations to operate properly, it is necessary that the shared controlchannel is transmitted well with a constant quality. Thus, it isnecessary that the transmission power of the shared control channel isproperly controlled. But, the above-mentioned transmission power controlmethod of the circuit switching type cannot be used as it is, and auseful method is not yet established.

An object of the present invention is to provide a base station, amobile station and a power control method for controlling transmissionpower of a shared control channel using a method suitable for packetswitching type communication.

Means for Solving the Problem

In the present invention, a base station, is used, that includes: meansthat derives a transmission power of a mobile station based on receivequality of an uplink pilot channel; means that reports the derivedtransmission power to the mobile station; and means that receives acontrol channel transmitted by the mobile station according to thereported information.

Effect of the Invention

According to the present invention, transmission power of the sharedcontrol channel can be controlled using a method applicable to packetswitching type communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of a base station according to anembodiment of the present invention;

FIG. 2 shows a schematic block diagram of a mobile station according toan embodiment of the present invention;

FIG. 3 is a flowchart showing a transmission power control methodaccording to an embodiment of the present invention;

FIG. 4 is a diagram showing an example of correspondence relationshipamong CQI, MCS number and transmission power;

FIG. 5 is a diagram showing an example of correspondence relationshipamong CQI, MCS number and transmission power;

FIG. 6 is a diagram showing mapping examples of a pilot channel;

FIG. 7 is a diagram showing information items that are included in anuplink shared control channel;

FIG. 8 is a diagram showing a resource assignment example of an uplinkshared data channel;

FIGS. 9A-9D show a plurality of candidates considered when assigning aband;

FIG. 10 is a schematic diagram on operation principle of AMC;

FIG. 11 is a flowchart showing a transmission power control methodaccording to an embodiment of the present invention;

FIG. 12 is a diagram exemplary showing correspondence relationshipbetween receive quality and transmission power;

FIG. 13 is a diagram showing information items included in a downlinkshared control channel;

FIG. 14 is a diagram showing an example of power control according to anembodiment of the present invention;

FIG. 15 is a diagram showing radio resources and a unit of coding.

DESCRIPTION OF REFERENCE SIGNS

-   11 modulation and coding unit-   12 multiplexing unit-   13 radio unit-   14 transmission power determination unit-   21 radio unit-   23 demodulation and decoding unit-   24 pilot channel processing unit

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

According to an embodiment of the present invention, relative orabsolute power by which the mobile station needs to change itstransmission power is derived based on relationship between receivequality of an uplink pilot channel and receive quality that a controlchannel needs to satisfy or a transmission power value of the pilotchannel. Thus derived power is reported to the mobile station, so thatuplink transmission power is properly controlled. Accordingly, withoutusing the transmission power history over a past continuous time, themobile station receives an instruction on transmission power from thebase station each time when sending a packet so as to be able to adjustthe transmission power.

When the mobile station has not yet received the instruction, an uplinkpilot channel is transmitted after a procedure. In the procedure, apilot channel and a transmission power is reported to the mobile stationusing a downlink, and the mobile station derives the transmission powerbased on an average propagation loss between the mobile station and thebase station. The uplink pilot channel is transmitted using the derivedpower, and it is received by the base station. Accordingly, the basestation can properly determine a transmission power of the mobilestation of next time based on the pilot channel transmitted from themobile station.

The propagation loss may be derived from receive quality of a downlinkpilot channel and the transmission power value.

According to an embodiment of the present invention, the base stationreceives both or one of a first pilot channel in which a symbol mappingpattern is constant and a second pilot channel in which a symbol mappingpattern is variable. By preparing a plurality of kinds of uplink pilotchannels, both of channel estimation accuracy and transmissionefficiency of information can be considered.

According to an embodiment of the present invention, the mobile stationthat is transmitting traffic data is caused to transmit the controlchannel using a power derived based on the uplink pilot channel. Themobile station that is not yet transmitting traffic data is caused totransmit the control channel using a power derived based on the averagepropagation loss. Since the number of mobile stations that aretransmitting traffic data is relatively small, efficiency of powercontrol can be improved by applying the CQI based TPC only for themobile stations.

The base station may further includes means that determines a frequencychunk usable for the mobile station to transmit traffic data anddetermines a transmission power of the mobile station. The transmissionpower and the frequency chunk may be determined such that thetransmission power exceeds a predetermined threshold and that morechunks are used. Accordingly, resources of the shared data channel canbe easily and properly assigned.

A base station according to an embodiment of the present inventionincludes means that transmits a common pilot channel; means that derivesa plurality of transmission powers of a shared control channel based onreceive quality of a plurality of common pilot channels reported by anuplink; and means that reports the shared control channel to a pluralityof mobile stations using the derived transmission powers.

The derived transmission powers may be separately reported to the mobilestations receiving traffic data. Accordingly, transmission power can becontrolled for each mobile station. One of the derived transmissionpowers may be reported to the mobile stations that are receiving trafficdata. Accordingly, the plurality of control stations can be controlledwith a same transmission power. The transmission power may be atransmission power corresponding to a mobile station that reports theworst CQI among the plurality of mobile stations.

The shared control channel may be reported to a mobile station that isnot receiving traffic data using a predetermined transmission power.Accordingly, transmission power control for the shared control channelcan be performed also for mobile stations that desire only transmissionof the uplink traffic data.

The base station may include a coder for coding data for one or moremobile station as a unit, and the data for one or more mobile stationmay be transmitted using a same transmission power. By aligning the unitof coding with the range of data for which same transmission powercontrol is performed, a combination of strength of error correctioncapability and excess or deficiency of transmission power can beproperly set. For example, coding (decoding) can be simplified withoutexcess or deficiency of power, and on the other hand, transmission powercan be made large while error correction capability is high.

Embodiment 1

In a downlink, a common pilot channel is announced to all users from abase station, and a mobile station that desires downlink datacommunication reports receive quality of the common pilot channel to thebase station, so that it can be expected that the base stationdetermines a transmission power of the downlink shared control channel.However, in an uplink, the common pilot channel cannot be used. Thisembodiment is contrived in view of the problem. In the following, atransmission power control method for an uplink shared control channelin the packet switching type mobile communication system is described.

FIG. 1 shows a base station according to an embodiment of the presentinvention. The base station includes a modulation and coding unit 11that performs multilevel modulation on data to be transmitted andperforms channel coding, a multiplexing unit (MUX) 12 that multiplexes amodulated signal and a pilot channel, and a radio unit (RF) 13 thatconverts an multiplexed signal to a signal format for transmitting froman antenna, and further includes a transmission power determination unit14 that determines a transmission power of a mobile station based oninformation received from an upper apparatus of the base station or fromanother mobile station or based on base station data.

FIG. 2 shows a mobile station according to an embodiment of the presentinvention. The mobile station includes a radio unit (RF) 21 thatconverts a signal format of a signal received by an antenna, ademultiplexing unit (DeMUX) 22 that demultiplexes a pilot channel andother channel from the received signal, a pilot channel processing unit23 that performs channel estimation using the pilot channel and performsmeasurement of transmission loss and the like, and a demodulation anddecoding unit 24 that demodulates the received data and performs errorcorrection decoding.

FIG. 3 shows a flowchart showing an uplink transmission power controlmethod according to an embodiment of the present invention. In thisembodiment, a shared control channel of a fixed information rate and ashared data channel of a variable rate are prepared as uplink channels.The transmission power control method described below can be used forboth of the shared control channel and the shared data channel. Sincethe transmission rate of the shared control channel is constant, it isessential to control the transmission power of the mobile station forcontrolling receive quality of the shared control channel. On the otherhand, for controlling receive quality of the shared data channel, therea choice of adjusting the transmission rate in addition to controllingthe transmission power of the mobile station. The transmission rate canbe adjusted by changing the number of levels of the multilevelmodulation or changing a coding rate of data. By the way, although thetransmission rate of the shared control channel is fixed to be constantin this embodiment for simplifying explanation, the transmission rate ofthe shared control channel may be changed in another embodiment.

In step 1, a downlink pilot channel is transmitted from the base stationto the mobile station, and a transmission power P_(t) of the pilotchannel is also transmitted via an annunciation channel or a broadcastchannel (BCH).

As indicated as step 2, the mobile station receives the downlink pilotchannel and the transmission power for a period to calculate an averagepropagation loss L. The propagation loss L is mainly determined bydistance variation and shadowing, and in general, the propagation loss Lis not largely different between uplink and downlink when being averagedover a proper time. For example, by averaging the receive quality over arelatively long period such as a period of one or more frame, influenceof instantaneous variation such as fading is removed. FIG. 10 exemplaryshows a relationship between instantaneous receive SIR and an averagereceive SIR. In this embodiment, although the receive quality ismeasured as SINR, it may be measured as SIR, or measured as other amountindicating quality. A target quality SIR_(t) that the base station aimswhen the base station receives the uplink channel is represented as afollowing equation.SIR _(E) =P _(up) +L−I ₀ [dB]In this equation, P_(up) indicates a transmission power (the controlobject at present) transmitted by the mobile station, I₀ indicates aninterference power for an uplink channel observed at the base station.The propagation loss L is represented as a difference between thetransmission power P_(t) in the base station and the receive power P_(r)in the mobile station. The annunciation channel announced from the basestation includes the transmission power P_(t) at the base station, theuplink interference power I₀ and the target quality SIR_(t).

In step 3 of FIG. 3, a pilot channel is transmitted from the mobilestation to the base station. The transmission power at this time is apower that compensates for propagation loss calculated in step 2, and isnot a power that compensates for instantaneous fading received on anuplink propagation route.

In step 4, the base station measures a difference between the receivequality (receive SINR) of the received uplink pilot channel and therequired quality (required SINR) expected for the pilot channel. Thepower indicated by the difference (power difference) indicates a poweramount (relative power value) by which the mobile station needs tochange its transmission power from the current value such that qualityof channel received by the base station becomes the required quality.When deriving the power difference, the base station may use a table onreceive SIR, required SIR, MCS number and power difference by whichpower should be changed from the current value. The MCS number specifiesa combination of the number of levels of multilevel modulation and acoding rate. FIG. 4 shows a table example defining a correspondencerelationship among channel status information (CQI: Channel QualityIndicator) reported from the base station to the mobile station, MCSnumber and transmission power of the mobile station. The channel statusinformation is measured as SIR typically. In the example of FIG. 4, MCSnumber and transmission power can be derived based on CQI (SIR) measuredby the base station and reported from the base station. FIG. 5 shows atable example that can be used in a case where MCS number, instead ofthe CQI information, is reported from the base station to the mobilestation. FIGS. 4 and 5 show merely examples of a table used fordetermining the transmission power, and the transmission power may bedetermined based on other correspondence relationship.

In step 5, the base station reports, to the mobile station, the powerdifference by which the mobile station needs to change its transmissionpower from the current value using a downlink control channel.

In step 6, the mobile station adjusts the transmission power based onthe instructed information reported by the control channel. Theadjusting amount in this case is different from one in control by TPCbit (not up and down by 1 dB), but is an amount for adjusting thecurrent value to a target value at one time.

In step 7, the control channel is transmitted using an adjustedtransmission power. This transmission power is a value for compensatingfor not only the propagation loss but also minute variation such asfading. After that, by repeating the procedure from the step 3 to thestep 7 or repeating the procedure of steps 7, 4 and 6 for each packet,an uplink transmission power suitable for the mobile station can beproperly kept. However, in the repeated step 3, a pilot channelaccompanying the uplink control channel is used.

Embodiment 2

In the second embodiment of the present invention, processes in steps 3,4 and 5 in FIG. 3 are different. Since processes of other steps are thesame, overlapping explanations are not provided.

In step 3, the mobile station transmits a transmission power value of apilot channel in addition to transmitting the pilot channel to the basestation.

In step 4, the base station measures receive quality (receive SINR) ofthe received pilot channel. The base station compares the receivequality and the required quality, and calculates a power valueindicating the difference. A sum of the power value and the transmissionpower value indicates an absolute value of a power by which the mobilestation transmits a channel such that quality of the channel received bythe base station becomes the required quality. In the same way as thecase of embodiment 1, the power (power difference) indicated as thedifference indicates a power amount (relative power amount) by which themobile station needs to change its transmission power from the currentvalue such that quality of the channel received by the base stationbecomes the required quality.

In step 5, one or both of the relative power value and the absolutepower value is reported from the base station to the mobile stationusing a downlink.

In step 6, the mobile station adjusts the transmission power accordingto the instructed information reported by the control channel.

In step 7, the control channel is transmitted using the adjustedtransmission power. After that, by repeating the procedure from the step3 to the step 7 or repeating the procedure of steps 7, 4 and 6 for eachpacket, the uplink transmission power suitable for the mobile stationcan be properly kept.

Embodiment 3

The pilot channel of the uplink is an individual pilot channel that isdifferent for each mobile station and that is used for channelestimation, receive quality measurement, synchronization acquisition andthe like for the uplink. For the purpose of precisely monitoringcommunication status that changes every moment, it is better to transmitmany pilot channels. However, since the pilot channel is a known signal,the more the transmission amount of the pilot channel is, the more thetransmission efficiency becomes lowered. In addition, it is notnecessary to perform all of the channel estimation, receive qualitymeasurement, synchronization acquisition for uplink with same frequency.

From this viewpoint, in the third embodiment of the present invention,two types of uplink pilot channels are prepared, in which one is areference pilot channel that does not necessarily accompany the sharedcontrol channel, and another one is a pilot channel for channelestimation that accompanies the shared data channel.

The reference pilot channel may be used for channel estimation, receivequality measurement and synchronization acquisition for uplink, and itis similar to conventional one in terms of purpose of use. However, itis different from conventional one at least in the point that it istransmitted while transmission power control of the embodiments 1 and 2are being performed such that the receive quality is kept. In addition,it is necessary to estimate the channel so as to compensate for thepropagation route for demodulating the shared control channel. For thatpurpose, the reference pilot channel is transmitted accompanying theshared control channel. On the other hand, for measuring uplink receivequality, the reference pilot channel may be transmitted independentlywithout accompanying the shared control channel. However, the mappingposition of the symbol is fixed beforehand as one kind. FIG. 6(A) showsa situation in which the reference pilot channel accompanying the sharedcontrol channel and the independent reference pilot channel aretransmitted.

The pilot channel for channel estimation accompanies the shared datachannel and is used for channel estimation. (B)-(D) in FIG. 6 showexamples of mapping of the pilot channel for channel estimation. Sincethe mobile station can move at various high and low speeds, there may bea case in which time variation of channel status is large depending onthe mobile station. In this case, as shown in FIGS. 6(C) and (D) insteadof FIG. 6(B), many pilot channels for channel estimation are mapped inthe time axis direction so that channel estimation accuracy for a usermoving at high speed can be improved. For a mobile station that is notmoving at high speed, by mapping the pilot channel for channelestimation as few as possible, transmission efficiency for informationcan be improved. Since the pilot channel for channel estimation istransmitted or not transmitted, it can be referred to as a pilot channelfor capturing a reference pilot channel that is always beingtransmitted. According to the present embodiment, by providing aplurality of types of pilot channels and by adaptively mapping themaccording to use purpose or communication situation, channel estimationaccuracy and information transmission efficiency can be improved.

Embodiment 4

As mentioned above, in the mobile communication system, there are notonly a mobile station to which radio resources are actually assigned butalso a mobile station that desires assignment but to which radioresources are not yet assigned. Such a situation occurs in both ofuplink and downlink circuits. Therefore, the shared control channelincludes information on these various statuses.

FIG. 7 shows information items that may be included in an uplink sharedcontrol channel. In the control information shown in four lines of(1)-(4), (1) and (2) indicate information on downlink data transmissionby the shared data channel, and (3) and (4) indicate information onuplink data transmission by the shared data channel.

The item (1) indicates information of a response transmitted by a mobilestation when the mobile station that is actually performing downlinktraffic data transmission receives a downlink shared data channel. Whenthe mobile station can properly receive the downlink shared datachannel, the mobile station returns an acknowledgement (ACK) to the basestation, and when the mobile station cannot properly receive thedownlink shared data channel, the mobile station returns a negativeacknowledgement (NACK) to the base station.

The item (2) indicates CQI information reported, to the base station, bythe mobile station that is not currently performing downlink trafficdata transmission but wants to perform data transmission in the future.The mobile station that desires to perform the uplink data transmissionmeasures receive quality of a pilot channel included in the annunciationchannel, and reports the measurement result as the CQI information tothe base station to request scheduling of next time.

The item (3) indicates information accompanying the uplink shared datachannel transmitted by the mobile station that is actually performinguplink traffic data transmission. This accompanying information is usedfor demodulation of shared data channel in the base station, forexample. More particularly, the accompanying information may includemodulation scheme, transport block size, retransmission controlinformation, and identifier of the mobile station and the like. Themodulation scheme is information for specifying a scheme such as QPSK,16 QAM and the like, and it may be represented as a number of levels ofmultilevel modulation. The retransmission control information mayinclude, for example, a process number for specifying a position of apacket in hybrid ARQ (HARQ), a redundancy format of a retransmitted bit,a new data indicator indicating whether a packet is new data or aretransmitted packet, or the like.

The item (4) indicates information reported to the base station by amobile station that is currently not performing traffic datatransmission but desires to perform data transmission in the future.This information may include information on a transmission power or abuffer status of the mobile station. For example, transmission powerinformation may include information indicating how large a power is bywhich the mobile station transmits the shared control channel,information (maximum transmission power) indicating how large the poweris at the maximum by which the mobile station can transmit it, or thelike. The buffer status may be represented as a data amount (a fillingfactor of a buffer) stored in a transmission buffer of the mobilestation. For example, the larger the data amount is, the larger thepriority of the scheduling may be set.

In the present embodiment, the base satiation determines which of theitems (1)-(4) corresponds to transmission contents of the shared controlchannel. As a result, as to a mobile station ((1), (3)) that is actuallyperforming traffic data transmission, the transmission power of theuplink shared control channel is controlled by the method described inthe embodiment 1 or 2. That is, the base station measures receivequality of a pilot channel received from the mobile station, anddetermines and reports the transmission power of the mobile stationaccording to the quality, so that the mobile station transmits theuplink shared control channel according to the reported information(this transmission power control method is to be referred to as “CQIbased TPC” for the sake of convenience).

On the other hand, as to a mobile station ((2), (4)) that is notcurrently performing uplink traffic data transmission but desires toperform the data transmission in the future, the transmission power ofthe uplink shared control channel is controlled by the method describedin steps 2 and 3 in FIG. 3. That is, the mobile station receives thepilot channel and the annunciation channel for a period so as tocalculate an average propagation loss, so that the uplink shared controlchannel is transmitted to compensate for the propagation loss andcompensate for interference power at the base station (this transmissionpower control method is to be referred to as “slow TPC” for the sake ofconvenience).

Since the transmission power is adaptively changed at every moment inthe CQI based TPC, calculation load for determining it is large.Therefore, if control of the transmission power of the uplink sharedcontrol channel is performed based on the CQI based TPC for all of themobile stations, there is a fear that calculation load and delay in thebase station become very large. On the other hand, as to the uplinkshared control channel for the mobile station, corresponding to (2) and(4), that is not yet performing traffic data transmission, theimportance is lower than that corresponding to (1) and (3). For example,when the acknowledgement (ACK) of retransmission control is erroneouslydetermined, useless traffic increases to exert a bad influence on thesystem. But, even though the buffer status of the mobile station iserroneously determined, large bad effect does not arise. In addition,there is a possibility that the number of mobile stations related to (2)and (4) becomes far larger than that of mobile stations related to (1)and (3). From this viewpoint, in the present embodiment, the CQI basedTPC is performed for the mobile stations related to (1) and (3), so thataccurate transmission power control that can address instantaneousfading variation is performed. Then, slow TPC is performed for themobile stations related to (2) and (4) in which instantaneous fading isnot compensated for, and slow transmission power control is performedsuch that signal quality is maintained averagely. Accordingly, the CQIbased TPC described in embodiments 1 and 2 can be efficiently used.

Embodiment 5

FIG. 8 indicates a radio resource assignment example for an uplinkshared data channel according to a fifth embodiment of the presentinvention. Each procedure shown in FIG. 8 is executed in the basestation. In the present embodiment, there is a mobile station that isactually transmitting traffic data using an uplink shared data channel.This mobile station transmits the uplink shared control channel or thepilot channel or the like including the information item of (3) shown inFIG. 7 in the embodiment 4. The base station receives the pilot channeltransmitted from the mobile station, and the flow of FIG. 8 goes to step10.

In step 10, receive quality of the pilot channel is measured as CQIinformation.

In step 12, a band of the uplink shared data channel for the mobilestation is determined based on the measured CQI information and thetransmission power information received from the mobile station. In thepresent embodiment, the usable band is divided into a plurality offrequency blocks each including one or more sub-carrier. Typically, thepresent invention is used for a radio communication system of anorthogonal frequency division multiplexing (OFDM) scheme. The frequencyblock is also referred to as a frequency chunk or simply a chunk. One ormore frequency chunk may be used as various references such as a unit ofresource assignment, a unit of retransmission, or a unit of coding. Inthe present embodiment, one frequency chunk is set as a unit of resourceassignment.

FIGS. 9A-9D show a plurality of candidates considered when assigning aband. The lateral axis of each figure corresponds to frequency f, andthe vertical axis corresponds to power P. As shown in FIG. 9A, a band of10 MHz is divided to four frequency chunks of 2.5 MHz. In step 12 ofFIG. 8, resources are determined such that the power becomes greaterthan a power threshold P_(th) derived from the transmission powerinformation of the mobile station and that a band as wide as possible iskept (the band is determined such that the transmission power per onechunk is equal to or greater than the threshold and that the bandoccupies a wider transmission bandwidth.) For example, as totransmission power of the mobile station reported from the mobilestation, assuming that relationship between the power threshold P_(th)and the frequency chunk becomes each of ones in FIG. 9. In this case, inthe resource assignments shown in FIGS. 9A and 9B, since the power isless than the threshold, these two candidates are excluded. Althougheach of FIGS. 9C and 9D exceeds the threshold of the power, since theone shown in FIG. 9C occupies a wider frequency band, it is determinedto be an optimal resource assignment method.

In step 14 of FIG. 8, a MCS number corresponding to the power determinedin step 12 is selected.

In step 16, information on the MCS number derived in step 14, the band(information for specifying frequency chunk) determined in step 12 andtransmission power and the like is reported to the mobile station viathe downlink shared control channel. Accordingly, the mobile station canproperly transmit the uplink shared data channel. According to thepresent embodiment, as shown in FIG. 10, an adaptive modulation andcoding (AMC) scheme is adopted for addressing instantaneous fading, andthe MCS number is adaptively updated for each TTI in the example shownin the figure. By adopting AMC in addition to the slow TPC for bringingthe average receive SIR close to a target value, transmission quality ofthe uplink shared data channel can be improved.

Embodiment 6

Uplink transmission power control is described in the first to fifthembodiments, and a transmission power control method for a downlinkshared control channel is described in the sixth embodiment of thepresent invention. FIG. 11 is a flowchart showing a transmission powercontrol method according to an embodiment of the present invention. Asshown in step 112, the base station transmits a common pilot channel tomobile stations under the base station. The common pilot channel isdifferent from the pilot channel that is transmitted by each mobilestation via an uplink in that the common pilot channel is commonlytransmitted to all of the mobile stations. In step 114, the mobilestation measures receive signal quality as CQI information based on thereceived common pilot channel. The mobile station performing downlinkdata transmission reports the measured CQI information to the basestation using the uplink shared control channel in step 116. In step118, the base station determines a transmission power of the downlinkshared control channel based on the reported CQI information.Correspondence relationship between CQI information and transmissionpower shown in FIG. 12 is prepared beforehand. In step 120, the basestation transmits the downlink shared control channel using thedetermined power in step 118. Accordingly, the transmission power of thedownlink shared control channel can be determined based on the CQIinformation measured in the mobile station (this method is to bereferred to as “CQI based downlink TPC” for the sake of convenience).

FIG. 13 indicates information items that may be included in the downlinkshared control channel. These information items are largely classifiedas control information on downlink (left column) and control informationon uplink (right column). In addition, as shown in the left side of thefigure, the control information is largely classified as one on physicallayer (upper side) and one on layer 2 (L2) (lower side). The controlinformation on the downlink may include demodulation information,scheduling information and retransmission control information (HARQ).The demodulation information may include chunk assignment information,data modulation information and transport block size information. Thechunk assignment information is information for specifying a frequencychunk to be assigned to the downlink shared data channel to the mobilestation. The data modulation information is information for specifying amodulation scheme applied to the shared data channel, and it may bespecified by the MCS number. The transport block size informationindicates the number of bits that are transmitted, and can be associatedwith coding rate, and may be specified by the MCS number. The schedulinginformation may include identification information for identifying themobile station. The retransmission control information may include aprocess number of a transmitted packet, information indicatingredundancy format, and a new data indicator. The new data indicator isan indicator that indicates whether a packet is a new packet or aretransmitted packet.

The control information on the uplink may include a transmission powercontrol bit, a transmission timing control bit, a response bit of acontention-based channel, scheduling information and retransmissioncontrol information (HARQ) and the like. The transmission power controlbit and the transmission timing control bit indicate a transmissionpower and a transmission timing when transmitting the uplink shared datachannel, and these are determined and reported in scheduling by the basestation. The contention-based channel is a channel that may betransmitted from the mobile station to the base station withoutscheduling, and that is a channel that may cause contention between themobile station and another mobile station. The contention-based channelmay be a fast access channel and the like that includes a reservationpacket for requesting scheduling of the shared data channel, trafficdata of small size or control data. The control information includesresponse information (ACK/NACK), as response contents, indicatingwhether the contention-based channel that is transmitted from the mobilestation is properly received by the base station. The schedulinginformation may include identification information of the mobilestation, chunk assignment information, data modulation information andtransport block size and the like. These are similar to those describedfor the downlink, but these are different in that these are informationon the uplink. The retransmission control information (HARQ) includesinformation (ACK/NACK) indicating whether information transmitted fromthe mobile station to the base station is properly received by the basestation.

The mobile station that receives the control information on the downlink(left side) actually receives traffic data using the downlink shareddata channel. Therefore, since the number of that kind of mobilestations is the maximum number of users that can be assigned at most,the number of the mobile stations is not enormous. Therefore, the powerof the downlink shared control channel may be controlled using the CQIbased downlink TPC for each mobile station. Alternatively, “CQI baseddownlink TPC” for a mobile station corresponding to the worst CQI amonga plurality of mobile stations may be applied to other mobile stations.On the other hand, mobile stations that receive control information onuplink (right side) include mobile stations that desire to transmittraffic data using the uplink shared data channel currently or in thefuture. In the mobile stations, as to mobile stations that receivescontrol information on the downlink, power control using the CQI baseddownlink TPC may be performed for each mobile station like the case ofdownlink, or “CQI based TPC” for a mobile station corresponding to badCQI may be similarly applied to other mobile stations. However, theremay be many mobile stations (including mobile stations desiring onlyuplink data transmission) that do not receive downlink traffic datacurrently or in the future. In addition, since it is not necessary thatsuch mobile stations report receive quality of a received pilot channelto the base station as CQI information, it is difficult to perform CQIbased downlink TPC. In the present embodiment, as to such mobilestation, the shared control channel is transmitted using a power that isfixed to be a constant value.

FIG. 14 shows an example of power control according to the presentembodiment. In this example, users #1-#3 among five users are receivingdownlink traffic data. Therefore, the downlink shared control channelfor the user #1 may be controlled by the CQI based downlink TPC, and thetransmission power is indicated as P₁. For the users #2 and #3, in thesame way, they may be controlled by the CQI based downlink TPCseparately, and the transmission powers are represented as P₂ and P₃respectively. Alternatively, transmission power control for a mobilestation that reports the worst CQI among the three users may be appliedto other mobile stations. The transmission power P_(α) (α=1, 2 or 3) inthis case is made common to the users #1-#3. In addition, in the exampleshown in the figure, the remaining users #4 and #5 in the five users donot receive downlink traffic data, so that the downlink shared controlchannel for these mobile stations is transmitted using a fixed powerP_(FIX).

By the way, data transmitted from a transmitter is coded, modulated,mapped to radio resources, converted to a transmission symbol (OFDMsymbol, for example), and transmitted. Coding is performed for providingerror correction capability. Convolution coding or turbo coding or thelike may be performed. The unit for performing coding may be a chunk, ordata of a plurality of chunks may be coded as a whole. As for thepresent embodiment, it is desirable that coding is performed in units ofdata for which same transmission power control is performed. Forexample, when the transmission power control is performed for each user,it is desirable that coding is also performed for each user. Whentransmission power control is performed for three users as a whole, itis desirable that coding is performed for three users as a whole.

For example, in a situation described with reference to FIG. 14,assuming that resources of three users of users #1, #2 and #3 areassigned as shown in FIG. 15(1). One chunk is assigned to the user #1,three chunks are assigned to the user #2, and four chunks are assignedto the user #3. Coding is performed for each user, and each of threeranges of data each enclosed with a thick line is coded separately. Asto these pieces of data, three users are controlled by “CQI baseddownlink TPC” separately, and transmission powers are represented as P₁,P₂ and P₃ respectively. FIG. 15(2) also shows a situation in whichcoding and power control are performed for each user, but assignment ofchunk is different. In the example shown in FIG. 15(3), data of threeusers are coded as a whole, and a control method (CQI based downlinkTPC) for one of the users is applied to other users. The transmissionpower is indicated as P_(α) (α=1, 2 or 3), and is transmission power fora user that reports the worst CQI. By the way, the user number and theunit for bringing together in coding are merely examples, and variousnumbers may be adopted. Generally, the larger the unit for coding is,the higher error correction ability becomes, but calculation load tendsto increase. Therefore, in the example shown in FIG. 15(1), calculationload for coding and decoding is small, and transmission power isoptimally controlled without excess or deficiency. On the other hand, inthe example shown in FIG. 15(3), although calculation load for codingand decoding becomes large, large error correction ability can beexpected, and in addition, since power becomes excessive for two usersof the three users, improvement of data can be expected. From theviewpoint for simplifying processes and strengthening improvement ofquality, it is desirable to adopt same power control to data included inone unit of coding like the present embodiment.

The present application claims priority based on Japanese patentapplication No. 2005-174395, filed in the JPO on Jun. 14, 2005 andJapanese patent application No. 2005-241902, filed in the JPO on Aug.23, 2005, and the entire contents of them are incorporated herein byreference.

The invention claimed is:
 1. A base station comprising: a unitconfigured to derive a transmission power of a mobile station based onreceive quality of a known signal of an uplink; a unit configured toreport the derived transmission power to the mobile station; and a unitconfigured to receive a control channel transmitted by the mobilestation according to the reported information, wherein the base stationreports a known signal and a transmission power using a downlink, andreceives the known signal of the uplink that is transmitted with a powerderived by the mobile station based on an average propagation lossbetween the mobile station and the base station, and the base stationcauses the mobile station that is transmitting traffic data of theuplink to transmit a control channel of the uplink that includes atleast one of ACK/NACK and CQI using a power derived based on a pastknown signal of the uplink.
 2. The base station as claimed in claim 1,wherein the base station causes the mobile station that is nottransmitting traffic data of the uplink to transmit the control channelof the uplink using a power derived based on the average propagationloss.
 3. The base station as claimed in claim 1, wherein the basestation derives a relative power amount by which the mobile stationneeds to change a transmission power based on relationship between thereceive quality of the known signal of the uplink and receive qualitythat the control channel needs to satisfy.
 4. The base station asclaimed in claim 1, wherein the base station derives an absolute poweramount to which the mobile station needs to change a transmission powerbased on relationship between the receive quality of the known signal ofthe uplink and a transmission power value of the known signal.
 5. Thebase station as claimed in claim 1, wherein the propagation loss isderived from the receive quality and the transmission power value of theknown signal of the downlink.
 6. The base station as claimed in claim 1,wherein the base station receives both or one of a first known signal inwhich a symbol mapping' pattern is constant and a second known signal inwhich a symbol mapping pattern is variable.
 7. The base station asclaimed in claim 1, the base station further comprising: a unitconfigured to determine a frequency chunk usable for the mobile stationto transmit traffic data and determine a transmission power of themobile station.
 8. The base station as claimed in claim 7, wherein thetransmission power and the frequency chunk are determined such that thetransmission power exceeds a predetermined threshold and that morechunks are used.
 9. A mobile station comprising: a unit configured toreceive a transmission power using a downlink when a base stationderives the transmission power by which the mobile station needs tochange based on receive quality of a known signal of an uplink; and aunit configured to change its transmission power based on reportedinformation to transmit a control channel, wherein the mobile stationreceives a known signal and transmission power value using a downlink,and derives a transmission power based on an average propagation lossbetween the mobile station and the base station, and transmits the knownsignal of the uplink using the derived transmission power, and when themobile station is transmitting traffic data of the uplink, the mobilestation transmits a control channel of the uplink that includes at leastone of ACK/NACK and CQI using a transmission power derived by the basestation based on a past known signal of the uplink.
 10. The mobilestation as claimed in claim 9, wherein, when the mobile station is nottransmitting traffic data of the uplink, the mobile station transmitsthe control channel of the uplink using a power derived based on theaverage propagation loss.
 11. The mobile station as claimed in claim 9,wherein the mobile station transmits both or one of a first known signalin which a symbol mapping pattern is constant and a second known signalin which a symbol mapping pattern is variable.
 12. A power controlmethod comprising the steps of: deriving a transmission power of amobile station based on receive quality of a known signal of an uplink;reporting the derived transmission power to the mobile station; andreceiving a control channel transmitted by the mobile station accordingto the reported information, wherein a base station reports a knownsignal and a transmission power using a downlink, and receives the knownsignal of the uplink that is transmitted with a power derived by themobile station based on an average propagation loss between the mobilestation and the base station, and the base station causes the mobilestation that is transmitting traffic data of the uplink to transmit acontrol channel of the uplink that includes at least one of ACK/NACK andCQI using a power derived based on a past known signal of the uplink.13. The power control method as claimed in claim 12, wherein the basestation causes the mobile station that is not transmitting traffic dataof the uplink to transmit the control channel of the uplink using apower derived based on the average propagation loss.
 14. A power controlmethod comprising the steps of: receiving a transmission power using adownlink when a base station derives the transmission power by which amobile station needs to change based on receive quality of a knownsignal of an uplink; and changing its transmission power based onreported information to transmit a control channel, wherein the mobilestation receives a known signal and a transmission power value using adownlink, and derives a transmission power based on an averagepropagation loss between the mobile station and the base station, andtransmits the known signal of the uplink using the derived transmissionpower, and when the mobile station is transmitting traffic data of theuplink, the mobile station transmits a control channel of the uplinkthat includes at least one of ACK/NACK and CQI using a transmissionpower derived by the base station based on a past known signal of theuplink.
 15. The power control method as claimed in claim 14, wherein,when the mobile station is not transmitting traffic data of the uplink,the mobile station transmits the control channel of the uplink using apower derived based on the average propagation loss.